1. Field of the Invention
The present invention relates to a backlight module, especially to a direct backlight module and a liquid crystal display (LCD) using the same, whereby the undesired dark areas on the corners and/or edges of the display can be efficiently reduced, resulting in a uniform overall luminance.
2. Descriptions of the Related Art
Liquid crystal displays (LCDs) have become the most popular displays because of the light weight and good displaying quality. The backlight module is an important illumination structure of the LCD. Controlling the transmissive light provided from the backlight module in association with the liquid crystal cells in a matrix of a panel, and appropriately controlling switches, make the brightness and quality of the images presented on the display be determined. Light emitting diodes (LEDs) widely serve as the light source of the backlight module because of the low power consumption, light weight and high luminance. Therefore, LEDs have gradually become substitutes for fluorescent lamps when selecting light sources for the backlight module.
FIG. 1 is a perspective view of a conventional LCD, which comprises an LCD panel 30, a front frame 20 disposed on the LCD panel 30, a backlight module 10 having an LED array 103 disposed on a back bezel 101, and a frame assembly 102 disposed along the edges of the back bezel 101. The backlight module 10 is a direct type backlight module. There are a plurality of optical films 40 disposed between the LCD panel 30 and the backlight module 10 for enhancing the efficiency of light usage and luminance promotion. The optical films 40 can be diffusing films, prism films, acrylic films and/or light enhancing films.
Generally, the LCD panel 30 comprises an upper glass substrate, a lower glass substrate, and a liquid crystal layer (not shown) disposed therebetween. The upper glass substrate and the lower glass substrate can be a color filter substrate and an active (or passive) array substrate, respectively. The voltage difference between the upper and the lower glass substrates makes the liquid crystal in the liquid crystal layer rotate or tilt accordingly. Therefore, the light transmitting through the LCD panel 30 will be controlled and will then produce images on the LCD panel 30.
The LED array 103 can be constituted by individually packaging a plurality of single LEDs or by integrally packaging a module that has a plurality of LEDs. A printed circuit board (not shown) is electrically connected to the LED array 103 for supplying power. The LEDs of the LED array 103 can be red, green, blue, or white LEDs, depending on the requirements of the LCD panel 30.
The material of the frame assembly 102 and the back bezel 101 can be light reflective. The inner walls thereof can also be made of reflective materials or have reflective films adhered thereon to reflect the light projected from the LED array 103.
Nevertheless, there is no light source disposed on the corner or edge portions of the backlight module because the undesired dark areas may occur in those parts, thereby causing the brightness of the overall backlight module to not be uniform. Additional light sources that are disposed on the corner or edge portions of the backlight module make the design and manufacturing procedures more complicated. Thus, it is not facilitated to control the uniformity of the brightness by adding light sources at the edges and corners.